The field of chemical analysis has been assisted by the use of liquid extraction surface sampling. Liquid extraction-based surface sampling mass spectrometry (MS) employing spatially resolved confined liquid/solid extraction of the analyte(s) of interest from a surface is becoming an established analysis methodology. The increased use of this methodology is due in part to the realization that this sampling method provides unrivaled sensitivity compared to other ambient surface sampling techniques. Examples of such systems are shown in U.S. Pat. No. 8,084,735 to Kertesz et al; U.S. Pat. No. 8,384,020 to Jesse et al.; U.S. Pat. No. 8,486,703 to Van Berkel et al.; U.S. Pat. No. 8,637,813 to Van Berkel et al.; U.S. Pat. No. 8,519,330 to Van Berkel et al.; U.S. Pat. No. 8,497,473 to Kertesz et al.; U.S. Pat. No. 8,742,338 to Van Berkel et al.; and U.S. Pat. No. 6,803,566 to Van Berkel et al.; and U.S. Publication Nos. 2012/0053065 to Van Berkel et al.; 2011/0284735 to Van Berkel et al.; 2012/0304747 to Van Berkel et al.; 2014/0096624 to ElNaggar et al.; 2013/0294971 to Van Berkel et al.; 2014/0216177 to Van Berkel et al.; and 2014/0238155 to Van Berkel et al. In addition, spatially resolved, confined liquid solid/extraction of surface has been coupled with high performance liquid chromatography (HPLC) separation utilizing a wall-less liquid microjunction probe surface sampling concept to allow transfer of the sampled material for post-sampling processing (V. Kertesz, G. J. Van Berkel. Liquid microjunction surface sampling coupled with high-pressure liquid chromatography-electrospray ionization-mass spectrometry for analysis of drugs and metabolites in whole-body thin tissue sections. Anal. Chem. 2010, 82, 5917-5921; V. Kertesz, G. J. Van Berkel. Automated liquid microjunction surface sampling-HPLC-MS/MS analysis of drugs and metabolites in whole-body thin tissue sections. Bioanal. 2013, 5, 819-826; G. J. Van Berkel, V. Kertesz. Continuous-flow liquid microjunction surface sampling probe connected on-line with high-performance liquid chromatography/mass spectrometry for spatially resolved analysis of small molecules and proteins. Rapid Commun. Mass Spectrom. 2013, 27, 1329-1334). The best spatial resolution achieved was about 500 μm.
Recently a single capillary liquid junction extraction/ESI emitter named scanning probe electrospray ionization (SPESI) was introduced for surface analysis purposes. See U.S. Pat. No. 8,710,436 to Otsuka; U.S. Publication Nos. 2014/0070088 to Otsuka; US 2013/0341279 to Otsuka et al.; 2014/0070089 to Otsuka; U.S. 2014/0070093 to Otsuka; U.S. 2014/0070094 to Otsuka; U.S. 2014/0072476 to Otsuka; and 2013/0334030 to Otsuka et al.; Otsuka et al. Imaging mass spectrometry of a mouse brain by tapping-mode scanning probe electrospray ionization. Analyst, 2014, 139, 2336-2341; and Otsuka et al.; Scanning probe electrospray ionization for ambient mass spectrometry. Rapid Commun. Mass Spectrom. 2012, 26, 2725-2732. This geometry eliminates the aspiration/emitter capillary that is a primary factor in the ultimate resolution of any dual capillary, liquid junction surface sampling probe. A single capillary is used to supply solvent to form a liquid junction between the capillary and a sample surface. A bias voltage is applied to the solvent to generate an ESI from liquid that pools at the top of the capillary via capillary action and the force of the applied electric field. In the version most suitable for imaging, spontaneous vibration of the probe itself (termed tapping-mode) created an alternate liquid junction surface sampling/non-contact ESI situation at a rate of greater than 100 Hz. Data presented by Otsuka and coworkers indicated a sampling spot size and lane scan width of approximately 150 μm. As surface sampling probes become smaller and direct spraying from the probe is accomplished there is a need for a way to incorporate post-sampling sample processing to obtain more chemical information. The elimination of the aspiration capillary from these systems requires a different system to handle the extract.
The disclosures of the above-identified patents and publications are incorporated fully by reference.